Carrier-transmission systeii



Feb. 1927.

15" J. s. JAMMER CARRIER TRANSMISSION SYSTEM Filed Dec. 19.1924 3 Sheets-Sheet l v ZQFE@ lll.

f1 fuomL -Jwmpmm ZOFEW Feb. 15, 1927. 1,617,393

` J. s. JAMMER CARRIER TRANSMISSION SYSTEM Filed Dec. 19. 1924 3 Sheets-Sheet 2 STATION 1. y

#mw/arf l dam dwf/27er u 1,617, 9 Feb' 15 EL J. s. JAMMER 3 3 CARRIER TRANSMISSION SYSTEM Filed Dec. 19. 1924 3 Sheaets--Sheml 5 Patented Feb. 15, 1927.

PATENT QFFICE.

JACOB S. JAMMER, 0F CUMBEBLAND. MARYLAND, A.SSGNOR TO /'ESTERN ELECTRIC COTFANY, INCORPORATED, GF NEVI YORK, N. Y., A CORPORATION OF NEV YORK.

CARRIER-TRAQSIJIISSION SYSTEIYI.

Application tiled Deeembfr 19, 1924.

r`his invention relates to carrier wave transmission and particularly to carrier dispatch systems.

An object ot the invention is to provide a simple and eliicient. carrier system applicable to dispatch or order circuits, such as are used in train dispatching and the like.

ln accordance with one Yeature ot the invention means are provided in a carrier transmission system whereby any one ot several wey-stations in the system may signal and ta l: with any other specil'ic waystation in the system without interfering with the telephone or telegraph trattic normally associated with the wires connecting` the way-stations.

ln the system ot the invention a single master oscillator' located at one ot' the stations supplies carrier to the transmittingl and receiving;n circuits otl all the way-stations along the line. ln speech transmission. the master station uses an unbalanced modulator and transmits the unmodulated carrier and one side band, white at the other w ystations. balanced modulators are used to suppress the carrier and transmit a single side band to conunnnicatc between stations.

For callingy or signaling purposes, each ot the way-stations alone' the line has assigned to it adiil'erent Yfrequency which is not equal to the carrier lrequency. All ot these signaling `frequencies assigned to the various way-stations lie within the range ot' the band lilter used 'lor speech transmission, but are separated enough from each other to prevent 'talse signals. The master station is able to signal any one etl the other way-stations by simply changincI the trequcncy ot the master oscillator so that it equals the trequcncy normally associated with the specific waysstation signaled. .Any one et: the other way-stations may signal another way-station or the master station by uubalmuinn` its modulator and 'arising it to oscillate at a frequency equal to the Ytrequency ot the specitic station to he called. This signalingy frequency is received by all ot' the way-stations, but. in the case ot' the particular station assigned this `frequency for signaling' purposes, it passes trom a demodulator through a tuned circuit selective to it and is applied to a moiilulator. Tl c s an i 'icrease in the space current v.lulatcnj., which by .means et Serial No. 756,872.

lays is made to operate signaling equipment. lVhen the circuits are set up for speech transn'iission, however, the tuned circuit coupling the demodulator to the modulator is retuned to the carrier `Frequency.

in accordance with another teature ol: the invention` means are provided whereby sub` stantially no energy is absorbed from the line by the way stations along the line.

ln accordance with another feature, means are provided whereby when the master station is communicating with any one ot a certain group ot way-stations, carrier current is also Yfurnished to the way-stations ot another group so that they may communicate with each other.

Other Vfeatures and advantages of the invention will be clear trom the 'following' detailed description read in connection with the accompanying drawings, in which:

Fig'. l is a diagralmnatie view illustrating in simplilied 't'orm a carrier dispatch system embodying` the invention.

Fic'. 2 is a diagrannnatie view illustratingr in detail one ot the way-stations ot' the carrier dispatch system shown in Fig. l.

Fie'. il is a schematic view illustrating' a ino-.lilication ot' the system ot Figi. l.

Fic'. `t is a dfagrammatic View illustratinp in detail the master station ot the system ot Fic'. 3.

ln the various ligures ot the drawing similar reterence characters represent similar elements.

Referring' to Fig'. t a carrier dispatch system is shown comprising),l a plurality ot way-stations l, Q, 3 and Ll, connected across a transmission line ML. At station l. hereimrtter referred to as the master station. a vacuum tube oscillator O is shown, this oscillator' providing carrier tor all the waystations along; the line. The oscillator t) is connected to the input circuit ot a modulator hl.. A transmitter circuit 'lc1 is also connected to the input circuit ot the modulator M.. The outputcircuit ot modulator Mi connected through the hybrid coil H1. band litter RF1, hybrid coil H2. and band filter BF., to the transmi l sion line ML. l; receiving' circuit. comprising' a demudolator l)l and the receiver R. is also associated with the line ML tlufoue'h the hybrid col H.. An artiticfal nethe l\ X, is provided for the purpose o? l time.. c; the, line. .ft repeater' [ill circuit lll is inserted in the line between the band lilters RF1 and BF2 tlnfough the hybrid eOil tlg.

its the apparatus and circuits ot waystations 2, 3 and el, hereinafter reterreifl to as substations7 are practically identical, it will only be i'ieeessary to describe station 2. No oscillator is provided at this station7 the transmitting' and receiving); circuits or' each ot the substations receivingcarrier current Yfrom the line dL provided by the oscillator O at the master station. itrt station 2, a` t ansmitter circuit T2 is connected to the in put circuit ot the modulator 'lhe output circuit ot the modulator lllg is associated through the hybrid coil lflm band lilter BFM hybrid coil H: and haiul Vl'ilter BF2, with the line ML. 'lhc receiving' circuit comprising` the deniodulator and the receiver it is also associated .with lthe line ML through `the hybrid coil lll. A selective network TC couples the output circuit ot the deinmlulator D2 with the input circuit the modulator Mz. its at station l, a repeater circuit R2 is inserted in the line between the bandy filters llf1 and ltg through hybrid coil ll2, and an artificial network N2 is provided Yl'or balancing the line.

For the oscillator (l at station l.. any known type oit generator such as a acuuni tube oscillator' in which a tuned circuit is provided tor fletermining,- the 'frequency of its oscillations may be uset. rShe n'iodulator lill may be ot the type illustrated and described in the United States patent to van der BijA No. lflOfiQ, issued August 2li, 1920. rllhe niodulator may be ot the balzzn-ced vacuum tube type designed to suppress the unmodulated carrier such as is illustrated and described in the United States patent to Carson No. l,B-il,3(lii. ii sued June l5, 1920. rlhe demodulators l) DL, may be ot the balanced vacuum tube type sucl as illustrated. in ltigf. ell) of an article entitled Carrier Current telephony and tele;n':u:-hy"` by Messrs. Colpitts and Blaelurcll, published in the transactions ot the iimerican lnstitute of Electrica Engineers, vol. #lll1 lJl. lfhe repeater circuits lll and lli, are ol tht well known two-wayg onerlenient typea and are inserted in the line at earh. station Al'or the purpose ot nic-reusing the tiunsniittiiuj and reeeiy'ing` `grains. il repiater gain ot three miles 'is used so that the saine amount ot energy is returned to the line as is passed into the way-station circuit and therelore suhstai'itially no energy is absorbed troni the line by the waystations.

The band filters EF1 and Bti! at station l, lill?"l and Blfg a stat-ion 2, and the band t. .tilters at the other substations are identical, and designed to suppress all oit the coinponents et modulation except one side band, either the upper or lower as desiredg and the :her/usos unmodulated carrier. These filters and each ot the other filters shown throughout the system may be designed in accordance with the principles set 'forth in the United States patenA to Campbell No. lQQidll, issued ll/lay 2Q, 1917. Two ot these band litters are prei'feably used at cach station in order to secure the required balance ol the two hybrid coils at each station.

'.lhe selective network TC coupling the transmitting and receiving units ot station 2 is tuned to some 'frequency within the side band passed by the band lters at that statiom whirh 'frequency is not equal to the ear- '.ier frequency. 'lhis is the frequency normally assigned to the particular way-station and is used tor signaling purposes. :l dit- 'lferent frequency is assigned lo each waystation along' the line, all ot these frequencies being within the transmitted side band.

rthe details ot the carrier dispatch system shown in simplified torni in Fig. l and niodilieations thereot are illustrated in Figs. 2, 3 and 4l. 'lf he operation ot the system will be described in Connection with these ligures.

ln Fig. 2, the apparatus and circuits oit one of the substations of the system ot Fig. l, such as station 2, are shown in detail. As stated in connection with the description ot lfigi'. l, the main clen'ients .included at this station couiprif'se a tranimitter circuit T, adapted to be connected to the input circuit ol a modulator lil-2, a denuululator DJ, a selective network TC mupling;l the modulator lllL and the demodulator D2, receiver R associated with the output ot the demodulator lig, band iilters BF] and BF2, tor suppress` iup; one ot the sie e bands received trom the modulator M2, and the repeater circuit ll2 inserted in the line between the hand filters lill"1 and BF@ in addition to these elen'ients, signaling agiparatus ot any suitable liind such as the hell ll vand the lanip l2 operated by the rel: 's l) and lll, is associated with the output 'irruit olf the modulator illu, and a resonant circuit, con'iprising an iiuluctanre coil 1531 feedback resistance. lli and condenser l?, is adapted to be connected lo the modulator llfltb to maite it `fuiulfion as an oscillator tor sigign'iliugi' purposes.

,lhc operation ot the syiileui illustrated in Figs. l and will now he described. tlup lj) r).

lll)

.lill

ctnuienser i in the input circuit oll ,network TC. changing' the natural treduency ot net work Tt) to the 'arrier trctpiency instead ot the sienalim;` 'frequency normally assigned to this particular substation; second, it opens the battery lead 8, makilu;` it impossible toi' the fie'nalinel relay t) in they plate circuit ot modulator M2 to operate the sigaar ing equipment comprisingY the bell 11 and the lamp .l2 at this station.

To signal the distant n'aynslation. the variable condenser 1T in shunt to the coil 15 is adjusted until the -i'ireipiency at which one side et the monilaer L, oscillates espiais the lfretpiencyY assigned to the particular' substation it is desired to signnl. yihen, key 125 .is

operated. The operation ol'V key lli accoml ,Y n Y l l plis-nes three resi-.i z lirst, it establisnes an oiL rating circuit for lrelay 1l and thus shortcircuits the demodulator lg; second, it rcmore:l the short-circuit trom the coii 15; nml, third, it connects' the feed-back resistance 1G to the coil 15 and condenser 1T. As the modulator M2 is unoalancciL and the adjustment of the Variable condenser 1T has been made, the signaling; 'lreiiuency is transmitted trom the output cir 'uit ol' modulator` M2 through the transformer 18, hybrid coil HQ, band lilter BFl, hybrid toil HQ, mnd litter BF2 to the main line lilla, and is received by all ot the several eey-stations in cludin;l the station signaled.

[is the ap )aratus and circuits at all ot the way-stations except the master station are similar, the operation at the station signaled will be described also by rel'erringY to the circuit shown in lille. 2. The current ot the sien; frequency received trom the line V' "lt/2, hybrid will russes through band tilt `r L, coil Hg, band filter BFl, hybrid coil H1 and the transformer 19 to the input circuit of the demodulator D2. rllhis signalingY lre (pienza/f' is amplilied by demodulator l),k and by means ot' output transt'ormer 2t), selective network Tt", which in the ci se ol the particular station signaled is timed to the signalinler frequency, and t anst'ormer 21, is supplied to the input circuit ot the b i 'eo moduiaor Blz. '.lhe application ot the ne# nadine' voltage to the modulator )ig 'anses its space current to be incr iascd snllicl ntly to cani-ze the operation ot' thc relay t) in itsl plate circuit, which as relay -.l is nel opc"- ated` establishes an operating circuit Vtor relay lt). 'the operation ot relay l() rines the bell l1 and lights the lamp 12.

`ifhcn the station attendant, observing the signal, connects his transmitting circuit 'l2 to the modulator lil: by inserting plugl 1 into jack 2, relay v`t is operated which breaks the battery connection 8 to relay lO, extinguishing' tio lamp 12 and stopping; the bell 11 from ringing'. The operation ot relay in the manner previously described, also tunes the selective net-Work TC to the carrier freqncncy.

ll'hcn the station attendant originalnu?. the. call releases the signalingy key 123, the relay 1l releases also, removing' the short circuit across his receivinguniti. Also, the release ot key 13 shortecircuits the coil 15 and disconnects the feed-hack resistance 1li Ytrom the coil 15. The carrier circuits are then set up :fo that the attennants at the two stations may talk to each other.

in speech transmission, voice 'frequency potentials troni the transmitter circuit 'I2 meansA el the transformer 3 are applied :iilerentially to the eritl circuits ot the tubes 22 and 2? ot the modulator circuit lili. Carrier potential Ytroni the network TC is applied through the transtornur .211 to the common portion ot' the. input circuit oit the oilulator M2. In accordance with the well u wn action ot the balanc itl modulator` the niodulated carrier is suppressed in the tput circuit ot modulator M2, but the side and currents, resulting trein the inte ac- Yioi ot the carrie and speech frequency curare reproduced in the output circuit. ny means ot' the transformer 18 and hybrid coil HQ, the side band currents are passed to the band tilter BFl, which suppresses one ot the side bands. One side band, therefore. is transmitted by lh", through hybrid coil HQ and a similar hand lilter lill"2 to the line ML.

is explained in connection with Fic 1, a part et the line energy is picked ott by means o t Vthe hybrid coil lil/L, and amplified in the rettieater circuit R2 and returned to the line. its each station is connected across the'main line ML, 'he gain -an be so adjusted that yery little energy is absorbed by the way-station.

At the receivingI station, the` side band current is received trom the line ML and passes through hand filter lllg, hybrid coil llg, hand litter lltll, hybrid coil H, and transtormer 1S) to the demodulator Dg. The demodulatinl speech currents .in the output et the demodulator D2 are transmitted through the transformer Q0 and the low pass liler 25 to the receiyer ll.

The low pass lilter 2: `inserted in the receii'infl' circuit in order to elin'iinate the carrier whistle and other olriect'ionable high l'reduencics. network Qi is inserted in the transmitter circuit T: vtor the purpose ol iniprovine' tl e quality :nid reducing the load on the modulator ML..

The method ot Signaling' between the various suhstations along' the line described above is not applicable to signals sont out by the master station. rThe in ethod of signaling' used it.' the `master station will non' be described. ils shown in Fig. 1. when the operator at the master Station, station l nuts' la wishes to signal one oi the subsiutions.7 he nmy change the frequency ot the oseil-v lutor 0l` until it equals the Atrcurrency noi niully :issigned to the purticuhir substation u'ith which he desires to counnuuicutc. This 'frequency will be pussed by the deinoduletor und the selective network TC ot the substation signaled und will opezrte sienuling zur puratus at thut station in the manner described above in connection with il Q. ln the ense ot' signals received by the inestestution, the Quin ot the deuiodulutor ll'I muy be increased by an additional stage ci :11nplilication coupled lo the deinodulutor by .r tuned circuit, :1nd siggnzilincY uppurntus muy be operated by s relay in the second stage oit the receiving unit. rifhis :ulditionel er1-pnrutus. not shown in Fig. l, is illustretcd und described in detail in connection with the modified circuit ot Filer. ai. The circuit ot the muster station ot ling): n'iodiiir-f. in u nurnner which "Will be explained later, is shown in detail in Fig. afl-7 und its operation in speech transmission und signaling' iill be clear troni the desc 'iption in connection with that figure.

ln Fig. 3 is shown schematically u noodi- .licution ot the Currier dispatch system ot Fig. l. At station l. the muster station. two oscillators, @l und U2, euch producing;` e diiterent trequency or n. ditl'erent range oit lireouiencies, und tuo corresponding: l'mnrl 'ilters BE. und Blij. euch adapted to press u. dil'l'erent Afrequency bund uro used insteud ot the single muster oscillator @L und the single bend filter Bill nt the muster stztion es in Fig. l. A certain group ot substritions connected across the transmission line lilll'l, tor exemple, stations Q, l und inuy be allocated trequencies Within the rune'Y passed by bund lilter lll., while another group ot stations for emunple, stations h 5 und T, muy be allocated frequencies Within the runge passed by band .tilter A suitable switching' arrangement .is provided whereby when oscillator 01 is connected to the line lilly through modulstmdeinodulstor circuit MD und the bund tilt then oscillutor @E will be connected to tue line ML directly through its bund iiltcr ll liilen'ise. the switching :u'ruiucnient :iduiitcd lo connect the oscillutor (ll directlyY lo the liuc lllll through iis l :and iilter lili-l when oscillator O2 connected to the line Twill through the inodi1lutor-de1nodulutor circuit MD und the bund lilter Blf..

liowa it the nnister station is siglnilingr or talking Vith any one ot the sulzstutions 1l und 6, selective to frequencies Within 'the range passed by band Vtilter BF?. oscillsur-r (ll will be connected to line Mil throne/jh the inodulstor-den'iodulutor MD und thehund lter Bll`3. At the seine time oscillator will be connected directly to the line through its bend Elib,

`ined ulator lil 1inwees i undv 'i' selective to 'frequencies within thc rungc passed by bund 'iler BFM will still be supplied. 'with Varrier 'troni the oscillator l2 so that they muy signal to und talk with euch other. Likewise, when the muster stef tion, using' carrier 'from oscillator O2, is connected to the line `so su lo signal or tulk with stations il, und i, then stations 2, si und 6 Will be supplied with carrier tf1-oni oscillator (5,.

The circuits und s Witch ing; e.rrungeinents oi? the ster station shown in llliig. il :1re shown in detuil in lslig. al.

'llhe circuit shown in that shoun :it station l seccrul oscillutzr O2, u fecoid bend tilter f ,M A1nd lier/'s ffii ti und Si? here been added.

fl diilers .troni 0 l 1n 'that u 1i 2 en edditionu. stegeolfun )liticntionAl suitable site 1-1arlingiY apparut 1s such zu;

o und bell rl Il?, associated 'th the output ot' the det" ill. not shown in Fig'. l but re- '.,crrcd to in the description ot' that iigure, rre shown 1n detail 1n Fig. 4.

'illie operation ot the noditied system will non be described referring; to Fig. lllith the leys ffl., und til., in the normally unoperuted. positions shown, oscillator O1 is connected through trunstoriners 2S und 29 to the input circuit ot modulator lill und through transt'oriners 2S and il() to the input err-uitrit deiuodulutor DI, The output circuit ot modulator lli., by ineens transiornicr ill. und the input circuit ot deu'iodulutor l). by ineens ot trunsliornier lo nrc pip Si" f operated by reluys the lceys us shown y 1 oscillator @2 is con nectcd to the line l through its bund iilter llllr. rllheret'ore. the carrier frequencies produced by the oscilllutors @l und @E will both be present on the line lilou@ it' the operuitor ut the muster station Wishes to tall; with any ot 'the substutions seiective to a. frequency within the band passed by band filter llllx. to signal that station the variable condenser 2i' in the tuned circ-uit of oscilletor U, is udliusted so thut the inirticulur signaling' lrcquency is produced by the oscillzitor O1 undv trnnsiniltcd to the line Mii through the bund ii. `r l'll l`hc rnuiinir Frequency will be received by ull oi.' the substutions ulonn the line, und, in the luse oit cirrler circuits between the substution und t e nurster station muy tuen be set up in the manner described preriouiiily in connection with 2.

lli/lith the cerrier circuits set up, the carrier mire trein oscillator @l is supplied to the und is modulated with voice ieu all)

transformer 33. rlhe components of modulation in the output circuit of modulator M, comprising both side bands, and the unmodulated carrier Will be passed by transformer 3l and hybrid coil H, to band tilter BET YBand tilter Bill, will suppress one of the side bands and transmitthe other side band and the unmodnlated carrier to the demodulating apparatus of the distant substation and thence to its receiver. llleanwhile, the frequency produced by -oscillator O2, which is connected to the line ML through its band filter BFH-will also be received by all of the substations along the line, and in the case of the, particular group of stations, 3, 5 and 7, selective to frequencies Within the band passed by hand lilter Bil, may be used for signaling and communicating between stations, in the manner described in connection with Fig. 2.

In like manner, the operation of the keys 5 S2 and S, will connect oscillator O2 through modulator M1 and demodulator D1, hybrid coil H1 and band filter Blfi to the line WL, and oscillator O, directly to the line ML through its band filter BFS, thereby making it possible for the master station to signal and talk with any of the substations, 3, 5 and 7 in the group selective to frequencies Within the band passed by the band iilter BR, and also to provide carrier current to the other group of stations, Q, il and 6 selective to frequencies within the band passed by band filter BF, so that they may signal and talk with each other.

Any of the substations along the line may signal the master station by simply unbal` ancing its modulator and transmitting the particular signaling frequency assigned to the master station, in the manner described in connection with Fig. 2, which frequency will pass through either band filter, BF, or BEM depending upon its value, through the hybrid coil H, and transformer 32 to the input circuitof the demodulator D1. This frequency will be passed by the demodulator l), through transforn'ier 3l and the network TG2, which is selective to it, and will be amplitied by the amplifier A1. The conse quent increase in space current of amplifier A, will operate relay 85 in its plate circuit. The operation of relay 35 will close an operating circuit to light lamp 3G and operate relav 3T to ring bell 3S.

Although, in connection with the description of the various moditications of the sys4 tem embodying the invention, itwas stated that the signaling frequencies associated with the various way-stations of the system were to lie within the range of the band tilter used for speech transmisson separated enough from each other to prevent. false signals, it is to be understood, however, that signaling frequencies outside this range may be used, and the signaling current passed around the band filter through suitabi., tuned circuits.

The invention set forth herein is, of course, susceptible of varons iii niificfzitioiis and adaptations other than tnose shown, and the figures and description `given herein are to be taken merelyY as illustrative of the invention and are not to be considered as limiting its scope except as defined in the appended claims.

lVhat is claimed is:

l. In a carrier Wave system. a master station and a plurality of Way stations, means only at the master station to generate carrier wares and transmit them to said Way stations, means at each way station to modulate carrier Waves from the master station in accordance with signals and to transmit to another Way statfon modulation components only While suppressing transmission of the uninodulated carrier component, and means at each way station for combining Waves of the carrier frequency received from the master station with the modulation components received from another Way station to receive said signals.

2. ln a carrier Wave system, a lne, a inaster station and a plurality of way stationsI connected to said line, means only at the master station to generate carrier Waves and transmit them to said line, modulating and demodulating means at each Way station to receive carrier and sideband components from said line but to transni't only sideband components to said line, and an amplilier connected between the said means at each Way station and said line, each amplifier comprising means to return to the line carrier waves equivalent in amount to the carrier waves absorbed by said way station.

3.111 a carrier transmission system, a transmission line, a plurality of stations connected to said line, a high frequency source at one of said stations for supplying a carrier Wave to said line, means at a second of said stations for receving said carrier Wave from said line, means at said second station for modulating said carrier Wave in ai'fcordance with speech signals, means at said second station for suppressing the unmodulated carrier component and one side band component of said signal-modulated Wave, and for transm'tting the other side band component of said sigual-modulated wave to a third one of said stations, means at said third station for demodulating the transmitted side band component. means at said third station for selectively receivingl the speech signals from the dcmodulated Waves. means at said thfrd station for selecting the unmodulated carrier component from said demodulated wares, means at said third station for modulating the selected carrier component `with other speech signals, nieaus for suppressing` the umnodulated comsortent and one side baud component from said signal-modulated Wave produced at said third station, and for transmitting the other side band component of said signal-modulated Wave produced at said third station to said second station.

l. ln a signaling system, a transmission line, a plurality of stations connected to said line, means for supplying said transmis ion line Wth a Wave. of carrier frequency, means 'it one of said stations for receiving,` said carrier Wave, a. circuit associated with said receiving means normally selective to a frcquency not equal. to said carr'er frequency, means for tuning said circuit to said carrier frequency, a balanced-modulator circuit supplied With carrier from said selective circuit when tuned to carrier frequency, means for unhalancing said balanced modulator circuit to malte it function as an oscillator to transm't a signal over .said transmission line to a second one of said stations, means at said first-mentioned station to change the frequency of the transmitted sional to a signalinpv frequency normally ass ned to said second station, a signaliiu.r device at said second station, and .means at said second station responsive to the Wave of changer frequency received from saidfirst mentioned station to operate said signaling device.

5. A carrier transmission system comprising,` a transmission line, a high frequency source for supplyingl carrier to ad line, a plurality of Way-stations connected across said line receivin` carrier from said line, and means including a repeater circuit at one of said Way-stations arranged to return to said line substantally the same amount of energy as is absorbed from said line by said way-station.

(3. ln a carrier transmission system, a transmission line, a plurality of Way-stations comprisingv a master station and a plurality of substations, a source of carrier Waves at said master station, a second source of carrier Waves at said master station, said second source producing; Waves of a different range of frequencies than the first mentioned source, means at said master station to modulate the carrier Waves from either source in accordance with speech signals, a band filter at said master station, said hand filter beingi adapted to pass the unmodulatml carrier from said first mentioned source and frequencies within the range of 'the side hand produced by modulation of th i carrier Wz Je from said first mentioned source with speech signals, and to suppress all other frequencies a second band filter at said master station.. said second hand filter beine' adapted to pass the unmodulated carrier Ware from said second source and frequencies Within Vthe range produced by the modulation of Jthe nerr/gees carrier from said second source with .speech signals. and to siqV press all other frequencies, one group of said sugistations being;` selective to frequencies passed by said first; .mentioned band filter, a second grouiii of said stilistations being;Y selective to frequencies passed by .raid second hand filter, and switching` means adapted for associating` either of said sources with said line through the modulating` means and the hand filter passing' the freipiency generated by the associated source, While associating the other source with said line direct-ly through the otherband filter.

7. ln a transn'iission system, a transmis- .sion path over which carrier frequencies may be transmitted, a plurality of signaling' stations associated therewith, a high frequency source at one of said stations supplying carrier current to said line, means at. a second of said stations for receiving: said current from said line, means at said second station to modulate said carrier current with speech signals, and. to suppress the unmodulated carrier component, a hand filter at said second station adapted to pass over said line to a third one of said stations a definite band of frequencies of the modulated Wave., and to suppress all other frequencies, another hand filter at said third station adapted to pass frequencies Within the range of the transmitted band, and to suppress frequencies outside said range, means associated with said other hand filter to demodulate said transmitted hand, means associated With the output of the demodidating` means to selectively receive the speech signals from the demodulated Waves, a tuned circuit associated with the output of said demodulating means to select'I the carrier Wave from said deinodulated Wares, means at said third station to modulate the selected carrier Wave with other speech signals, and to suppress the unmodulated carrier, and means comprising said other band fiiter to transmit one side hand of the components of modulation to said second station.

Si. 'lhe combination in a high frequency signaling; system of transmitting; line. two sources of high frequency current of different frequencies, means for modulatinc the high frequency current from either or said sources in accordance with speech, a band filter inserted in said line, adapted to pass frequencies within the range of one side baud coi'irlfionent formed hy the modulation of the ci'urent from one of said sources with speech, and to suppress all other frequencies, a second hand lter inserted in said line adapted to pass frequencies Within the range of one side hand component formed hy the modulation of the current from the other of said sources With silice/sh. and to suppress all other frequencies. means for demodulating speech-modulated Waves received over said line through either ot' the hand filters, means associated with the output of the demodulating cans to selectively receive the speech signals troni the de A1111111- lated Wares, and switching' 111eans adapted to associate one of said sources with said line through the hand lilter adapted to pass its frequency when the other ot' ,said sourcesl is associated With the line tlirou 1 said modulating means, said deniodulatiiigmeans and the other oi said hand tilters.

9. tn a signaling system. a tran@ :sion line, a station associated with said line.. a source ot carrier Waves at. said s en. 1` eaas for changingthe frequency 11 said Wares 'from said source for signaling' puro-osos. means for supplying said er. 'er stares 'to said line coniprisine a band liller adfple'l to pass a delinite hand of 'Frequencies i11- cluding;1 said chang-'ed carrier 't' cque11q1'. :1 second station associated 111111 said second hand ilter at said second stat-'rea adapted to pass the sain(1 ha o t 'treqiwiiciw including' the carrier u'ave ot' changed Vtrenienqueney as the hand filter 1 tioned station, a signali device at said second station, a network 911111111111111 with said second hand lilter norinaily selective to the changed carrier treajaencyA a Vacuum tube Inodu ator at said second station 11ssociated with said network for ainpli'tying said Wave ot changed carrier 'trequencj' means 111 the output ot said modulator responsive to the anipiihcd ware of changed carrier frequency to ope ate said .1511111111151 device.

l0. In a signaling` sjstein a transmission line oYer which carrier current is supplied to 11 plurality ot stations, 11 station associated With said line` a facuuin tube deinodulator at said station, a hand vliter adapted to pass a delinite hand et '11111111011M cies, including' the frequency ot said carrier ware, supplying carrier current to said de n1odu1ator from said iine, a 111111111111 tune modulator, a network` norinaliy selective to a 'frequency Within lthe range ot the 11111111 passed hy said hand tilter other than thel carrier 'trceuenoy, coupling; the output ot said deinodulator with the input ot said 1nodu1ato1', nieans to retune said 111111.11111: 1o the carrier tfreducnc;T to suppl),v e111'1'1111'-cu1'- rent to said modulator, means comprising' an oscillating circuit to adapt said 11101111- lator to tunction as an osciilator for sig- 111111111y purposes, means to tune said oscillation circuit to control the 'ireduencyY ot the oscillation transmitted 11.1' said 111o 1u later through said hand filter over said line to a second ot' said stations. the transinited frequency heine' a signaiing ilreducnev 11'1thi11 the range of said oa 11d 1111er.y 11 second 11111111 tilter at said second station adapted to pass said signaling requency, 11 signaling; device at said second station, :1 netuor: associated will'. said second hand 1111er no1'- n1all7 seleciife to said signaling Yfreq11e/11er, :1 '111-1111111 tuhe modulator at said second station associated with said network tor 11111pli- 'tying` said ware ot signaling;` frequency, means in the output o1 said modulator responsive to the amplilicd ware o1 signaling` frequencyV to operate said signaling device.

ll. En a wave transmission system. a line, a station connected across said line, a source carrier oscillations at said station, 11i-cans at said station to modulate said carrier oshlations with speech variations, a hand tiiter at said station to suppress one side hand component, and to transmit the o hcr side hand component, and the uninodulated component of the s1eech-1nod11lated ware over said line, a second station connected across said line, a band lilter at said second station to pass said side band coniponent 11nd said uninodulated component o1" the transmitted Wave, and 'to suppress all other frequencieres, means at said second station to demodulate the carrier oscillations and the speech variations of said side hand component passed hy said hand filter at said second station, ineans associated with the output ot the deinodulating means to selective@Y receive said speech variations, a tuned circuit associated with the output o' said deniodulating ineans to select said carrier oscillations', ineans at said second station 'to modulate the selected wave with other speech variations, and to suppress the uninoduiated component of the modulated ware, and means to suppress one side band component and to transmit the other side hand component of said signal modulated ware generated at said second station to said tirs-t mentioned station.

l2. 1n a wave transmission system, a transmission line, a high frequency source to supply a carrier Wave to said line, a plurality oitl stations receiving said carrier wave from said line, nieans at one ot said stations to inoduiate said carrier ware in accordance with speech signals, and to suppress the unnioduiated component o1.'v the speech niodulaled wave, a hand til'ter 11tsaid station to suppress one ot the side band components ot said speech modulated wave, and to transinit the other side hand component ot said speech modulated Wave over said line to another ol' said stations, a hand filter at said other station to pass said transmitted side 11111111 component, means at said other station to deniodulate said speech signals and said carrier ware, ineans associated with the output ot said deinodulating' means to selcctireluv receive said speech signals, means associated with the output ot said deniodulatiuy; nieans to select said carrier wave, means at said other station to modulate the selected carrier ware vwith other speech signals. and to suppress the uninodulated c0111- poncnt o1'Y said speech modulated are genemied :it Said othei` Station, and :i sommi band :iliei at said other Station to supprime one side bami emnponent of ihe 'jenei'zimi wave, indio ti'iii'isriinit ihe ohei eiiie mV-.11i component of Said genei'aiefi wave over said line to the first mentioned siaien.

13. ln a earriei` transmission system, ii transmission line, L plurality of Stations connected to Said line, a high frequency source it one of said stations to supply :i carrier Wave to Said line, said eau-rien Waves being supplied to all of Said stations 'from said line, means at another of said stzitiens Leit/,eee

i0 mochiiate Said emu-ier Wavre in neem-(hline iviih Speech signals, and ie suppress The imniedi'lizifeii ezu'i'iei', means :it .mid Oihei' siziiien to suppress one side band. eoinpenent, and to transmit the other Side bami eoinyonent of ihe eignai-inodninied wwe over said line io zithiid siiion, und ineens; :i Said third eizitien to deniocluiute said eau-rien Wave te reproduce said speeeh signzzie.

lin witness wheieo, hereuiite smilie my nume this 17th day of Deeembei' A. D.,

JACOB S. Jiiiiiivmn. 

